A thermal titration apparatus has been developed which permits the study of the small and rapid temperature changes associated with the chemical kinetics of protein. A reaction cell with a volume of 1 m1 is maintained at a constant temperature (.005 degrees C drift in 2000 seconds). Acid or base is delivered at a constant rate and rapid mixing is accomplished with a constant speed (plus or minus 0.5%) stirring system. pH and temperature changes are recorded. Testing has determined that the temperature which is displayed on an x-y recorder, can be measured at 0.00025 degrees c per cm scale and the heat of reaction is similarly monitored at 0.0002 cal per cm scale. A differential version of the existing system is currently being developed which incorporates simultaneous optical measurements.